Particulate filters are utilized to remove particulate matter from an engine's exhaust flow. After an extended period of use, however, the particulate filter can become saturated with particulate matter, thereby reducing the functionality of the filter and subsequent engine performance. The collected particulate matter can be removed from the particulate filter through a process called active regeneration. Active regeneration is the burning away of trapped particulate matter at high temperatures, typically in excess of 600° C. These temperatures can be periodically achieved through engine control, electric grids, and fuel-fired burners located upstream of the filter to heat the exhaust flowing through the filter.
When a machine is stationary, active regeneration may be undesirable in certain circumstances, as it can heat the exhaust system too high for the immediate environment. For example, if the machine was to stop and remain stationary in or near a location of dry debris, it might be possible for the high regeneration temperatures of the exhaust system to ignite the debris. Thus, when the machine is parked or moving very slowly in these areas for extended periods of time, active regeneration is generally disabled and/or prohibited.
An exemplary system that selectively disables active regeneration is disclosed by U.S. Patent Publication No. 2007/0000241 (the '241 publication) by Funke et al., published Jan. 4, 2007. The '241 publication discloses a particulate trap system for use with a mobile machine. The particulate trap system has a particulate trap, a regeneration device, and a controller. The controller is configured to control the regeneration device based on input received from different sensors. For example, when regeneration of the particulate trap is required and the mobile machine is traveling at a speed greater than three miles per hour, the controller directs the regeneration device to elevate the temperature of the particulate trap to thereby burn away trapped matter. In contrast, when the machine's travel speed is less than three miles per hour, regeneration is completely disabled. The controller can similarly control the regeneration device based on an exhaust temperature, a selected gear ratio of an associated transmission (i.e., based on if the transmission is in neutral), and/or the activation of a parking brake. In this manner, regeneration can be halted or inhibited when the machine is substantially stationary.
Unfortunately, when active regeneration is completely disabled, subsequent regeneration events may be undesirably extended. That is, by completely disabling active regeneration, if even for only a short period of time, it may take a long period of time and a large amount of energy to re-elevate the exhaust to the regeneration temperature range experienced prior to the disabling. And, if the disabling is implemented frequently, as may be the case in stop-and-go applications, for example in vocational application such as waste management (garbage truck) and public transportation (bus) or in recreational applications (RVs), the time between disabling events may be too short for the exhaust temperatures to be raised to a level sufficient for complete regeneration of the particulate filter. When complete regeneration is not possible, it may be required to continuously attempt regeneration, which may result in further efficiency losses.
The disclosed exhaust system is directed toward overcoming one or more of the problems set forth above and/or other problems in the art.